Piezoelectric vibrator

ABSTRACT

A piezoelectric vibrator of a high impact resistance is attained. The piezoelectric vibrator according to the present invention has a piezoelectric vibrating plate formed so that a vibrating portion thereof be integral with a frame, and covers disposed on upper and lower surfaces of the frame and sealing the piezoelectric vibrating plate air-tightly. The covers have first recesses in the sections thereof which are opposed to such a section of the vibrating member that is between a base section thereof and a free end section thereof and have spaces between inner surfaces of the same recesses and a surface of the vibrating member, and second recesses having in the vicinity of the free end a space of a width greater than a distance between the first recesses and vibrating member.

BACKGROUND OF THE INVENTION

[0001] This invention relates to a surface mounting type piezoelectric vibrator.

[0002] A piezoelectric vibrator in which a vibrating portion and a frame are formed so as to be integral with each other is held at a frame portion between covers as shown in FIG. 6 has heretofore been known. In a piezoelectric vibrator of such a construction, covers 10, 20 have a recessed shape, and an inner surface (bottom surface of each of recessed portions) of the covers is generally made of a single flat surface (Refer to JP-A-5-199056).

[0003] Since each of the recessed portions on inner side of the covers in a related structure is thus made of a single flat surface, a free end 35 of a vibrating portion 30 impinges in some cases as shown in FIG. 6 upon one of inner surfaces 15, 25 of the covers 10, 20 when the vibrator falls to cause the vibrating portion to be bent due to an impact imparted at the mentioned time to the vibrating plate. When a specially strong impact is imparted to the vibrating plate, the free end impinges upon the inner surface of a cover strongly, so that the free end of the vibrating portion chips off. This causes a frequency constituting one of the important characteristics of the vibrator to be varied greatly in some cases. Incidentally, in a tuning fork quartz oscillator for timepieces, the standards of frequency deviation are about 10 to 20 ppm. On the other hand, when a chip occurs on a free end of a vibrating portion of the oscillator as mentioned previously, the frequency varies by not lower than several hundred ppm in some cases, this posing a big problem.

[0004] In addition, in order to solve such a problem as mentioned above, a deep and large space is provided on an inner side of the inner surfaces of the covers so that these inner surfaces are separated from the vibrating portion for the purpose of substantially preventing the free end of the vibrating portion from impinging upon the inner surface of a cover. Therefore, the thickness of the covers tends to increase, so that it becomes difficult to deal with a problem of the reduction, which is now strongly demanded, of the thickness of the vibrator.

SUMMARY OF THE INVENTION

[0005] In view of these circumstances, the present invention has been made so that a structure of a piezoelectric vibrator capable of preventing the occurrence of breakage ascribed to an impact imparted thereto of a vibrating portion be attained without increasing a total thickness of the vibrator. To provide such a structure, the invention forms inner surfaces of covers, which are used as a case for the piezoelectric vibrator, by surfaces having at least two-stage recesses. In this structure, the collision of a free end of a piezoelectric vibrator with an inner surface of the case can be prevented by increasing the depth of the two-stage recesses from the side of a base portion of a piezoelectric vibrating plate toward that of the free end section thereof, and providing the portions of the inner surface of the case which is on the upper and lower sides with respect to the direction of the thickness of the free end section of the vibrating portion with deeper recesses extending from the part of the inner surface of the case which corresponds to a lengthwise intermediate section of the vibrating portion of the piezoelectric vibrating plate to the part of the same inner surface which is beyond the fee end of the vibrating portion.

[0006] The depth of first recesses constituting shallower portions of the two-stage recesses accounts for 2% to 25% of the thickness of the covers, and that of second recesses constituting deeper portions of the two-stage recesses 25% to 60%. A difference in depth occurring on boundary sections between the first recesses and second recesses is set so that stepped sections of the recesses receives an intermediate section of the vibrating portion bent due to an impact imparted to the vibrator. When the stepped sections are formed, in the case of a vibrating plate fixed at one end thereof, in positions away from the fixed sections thereof by a distance corresponding to 40% to 80% of a length of the vibrating plate measured from the fixed section thereof to the free end thereof, excellent results are obtained.

[0007] According to such a method, the intermediate section of the vibrating portion impinges upon the depth-different sections between the first recess and second recess even when the vibrator falls to cause the vibrating portion to be bent due to an impact imparted to the piezoelectric vibrating plate, so that a further bend of the vibrating portion is prevented. Therefore, the free end of the vibrating portion does not impinge upon the inner surfaces of the covers, i.e., the chipping of the free end of the vibrating portion can be prevented.

BRIEF EXPLANATION OF THE DRAWINGS

[0008]FIG. 1 is a sectional view showing an embodiment of the piezoelectric vibrator according to the present invention;

[0009]FIG. 2 illustrates an operation of the embodiment of the present invention;

[0010]FIG. 3 is a sectional view showing another embodiment of the piezoelectric vibrator according to the present invention;

[0011]FIG. 4 is a sectional view showing still another embodiment of the piezoelectric vibrator according to the present invention;

[0012]FIG. 5 is a sectional view showing a further embodiment of the piezoelectric vibrator according to the present invention;

[0013]FIG. 6 is a sectional view showing a related art piezoelectric vibrator.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The present invention is adapted to prevent a free end of a vibrating portion from being chipped off when the vibrator falls to cause an impact to be imparted to the vibrating portion, by forming a two-stage flat surface on the inner side of each of covers used as a case.

[0015] Embodiments of the invention are described below.

[0016] (Embodiment 1)

[0017] A case for a surface-mounting type piezoelectric vibrator will be described with reference to the drawings. FIG. 1 is a sectional view showing an embodiment 1 of the present invention. A vibrating portion 30 of a piezoelectric vibrating plate is air-tightly sealed with covers 10 and 20. The cover 10 is provided with a first recess 16 and a second recess 17. Similarly, the cover 20 is provided with a first recess 26 and a second recess 27.

[0018]FIG. 2 illustrates an operation of the embodiment 1 of the present invention. A vibrating portion 31 bent when a vibrator falls to cause an impact to be imparted to a piezoelectric vibrating plate, an intermediate section of the vibrating portion 30 collides with a stepped section of a boundary between first recesses 16, 26 or second recesses 17, 27, and a further bend of the vibrating portion is prevented. Accordingly, a free end 35 of the vibrating portion 30 does not collide with an inner surface of a cover. Namely, the chipping of the fee end of the vibrating portion can be prevented. Regarding the sizes of each part of the vibrator according to this embodiment, a tuning fork type vibrating portion 30 is 2 to 4 mm in length and 80 μm to 150 μm in thickness, and first recesses 16, 26 and second recesses 17, 27 are 8 μm to 100 μm and 50 to 200 μm in depth respectively. The advantage according to the present invention is, of course, effective to, for example, a small-thickness vibrator, which is other than the tuning fork type vibrator, such as an AT cut thickness sliding mode vibrator.

[0019] In the piezoelectric plate fixed by the covers 10, 20 in this embodiment, the vibrating portion 30 and a frame type portion surrounding a circumference of the vibrating portion are formed so as to be integral with each other at a base end section of the vibrating portion. It is also possible to form the covers 10, 20 out of glass, and make anodic connection to the piezoelectric vibrating plate via a metal film provided on the frame type portion of the piezoelectric vibrating plate.

[0020] The piezoelectric vibrating plate has on both side surfaces thereof exciting electrode films for operating the piezoelectric vibrating portion.

[0021] (Embodiment 2)

[0022]FIG. 3 is a sectional view showing another embodiment 2 of the present invention. This embodiment constitutes an, example having third recesses 18, 28 on a fixed end side of a vibrating portion, and has the same effect as the embodiment 1. Although the embodiment 2 seems to be structurally complicated, the depth of third recesses and second recesses is equal, and this embodiment is identical with the first embodiment in that two-stage flat surfaces are provided on the inner side of covers.

[0023] (Embodiment 3)

[0024]FIG. 4 is a sectional view showing still another embodiment 3 of the present invention. This embodiment constitutes an example in which slightly rounded projections 19, 29 are provided instead of such first recesses 16, 26 as in the embodiment 2. When a certain stepped portion-forming method, such as a sintering method is used, first and second recesses are not formed by accurately flat surfaces but by such slightly rounded surfaces as are shown in the embodiment 3. Even such a structure can prevent the bend of the vibrating portion, and the chipping of a free end 35.

[0025] (Embodiment 4)

[0026]FIG. 5 is a sectional view showing an embodiment 4 of the present invention. This embodiment constitutes an example in which the present invention is applied to a vibrator of a structure in which a vibrating portion 30 is mounted on a base plate 40, which is formed out of a ceramic material and the like, by a fixing material 50 with the base plate 40 and a cover 11 air-tightly sealing the vibrating portion 30 with a sealing material 45. When the first and second recesses shaped according to the present invention are thus provided even in a vibrator formed by such base plate and cover, i.e. members of different materials and structures, the chipping of a free end 35 of the vibrator can be prevented.

[0027] When the present invention is executed as described above, the collision of the free end of the vibrating portion with the inner surface of the case can be prevented even when the vibrator falls to cause an impact to be imparted to the vibrating portion, and a large variation of a frequency constituting one of the important characteristics of a vibrator can also be prevented.

[0028] Moreover, covers having a deep and large space become unnecessary, so that a total thickness of the covers can be reduced. This enables the reduction of the thickness, which has recently been demanded strongly, of a vibrator to be dealt with. 

What is claimed is:
 1. A piezoelectric vibrator comprising: a base plate on which a piezoelectric vibrating portion is mounted; and a cover combined with the base plate and capable of being air-tightly sealed without hampering vibration of the piezoelectric vibrating portion, wherein the inner surface of the base plate and that of the cover have at least a two-stage recess respectively, parts on two stages of which have different depths increasing toward the portion of the mentioned inner surface which corresponds to a free end of the piezoelectric vibrating portion.
 2. A piezoelectric vibrator comprising: a piezoelectric vibrating plate in which a piezoelectric vibrating portion and a frame-like portion surrounding a circumference of the piezoelectric vibrating portion are formed so as to be integral with each other at a base end section of the piezoelectric vibrating portion; and a pair of covers combined with the piezoelectric vibrating plate via joint films provided on upper and lower surfaces of the frame-like portion, wherein the two covers have in inner surfaces thereof at least a two-stage recess respectively of different depths which increase from the portion thereof which corresponds to a base end section of the piezoelectric vibrating plate toward the portion thereof which corresponds to a free end section of the vibrating plate.
 3. A piezoelectric vibrator according to claim 2, wherein the covers are formed of glass.
 4. A piezoelectric vibrator according to claim 1, wherein the depth of the first shallower recess out of the two-stage recesses accounts for 2% to 25% of the thickness of each cover, the depth of the second deeper recess thereof accounting for 25% to 60% of the thickness of each cover. 